Tilt actuated liquid metal switch having a negative break angle

ABSTRACT

A tilt actuated liquid metal switch of the liquid metal to electrode type including a depressor arranged to be in engagement with the pool of liquid metal which is located on a surface of the switch normally maintained in a substantially horizontal position so as to interact with the surface tension of the pool and thereby provide a force in the deactuating mode of the switch such that it is adequate to overcome the other inherent forces to cause disengagement of the pool from the electrode prior to the horizontal position being attained.

United States Patent [1 1 Blair [11] 3,755,643 [451 Aug. 28, 1973 TILT ACTUATED LIQUID METAL SWITCH HAVING A NEGATIVE BREAK ANGLE [75] lnventor: Carl D. Blair, Freeport, 111.

[73] Assignee: Honeywell Inc., Minneapolis, Minn. [22] Filed: Apr. 23, 1970 [21] Appl. N0.: 31,243

[52] US. Cl. 200/220 [51] Int. Cl. I'IOIh 29/20 [58] Field of Search ZOO/152.7, 152, 61.47,

ZOO/33.1, 182-236 [56] References Cited UNITED STATES PATENTS 2/1941 Olson 200/33.1.X Engel et al 200/152 3,198,919 8/1965 Tettke, Sr. et a1 200/152 Primary Examiner-Herman J. Hohauser Attorney-Lamont B. Koontz and Philip J. Zrimsek [5 7] ABSTRACT A tilt actuated liquid metal switch of the liquid metal to electrode type including a depressor arranged to be in engagement with the pool of liquid metal which is located on a surface of the switch normally maintained in a substantially horizontal position so as to interact with the surface tension of the pool and thereby provide a force in the deactuating mode of the switch such that it is adequate to overcome the other inherent forces to cause disengagement of the pool from the electrode prior to the horizontal position being attained.

4 Claims, 7 Drawing Figures PATENTEDMIB28 ma 3.755543 I N VENTOR. CARL D. BLAIR ATTORNEY.

TILT ACTUATED LIQUID METAL SWITCH HAVING A NEGATIVE BREAK ANGLE The present invention is directed to a tilt actuated liquid metal switch of the liquid metal to electrode type wherein a pool of liquid metal is associated with a surface of the switch envelope normally maintained in a substantially horizontal position and wherein the elements are so arranged that in the deactuating mode the pOOl moves away from the switching electrode prior to the surface attaining a horizontal position.

In the conventional tilt actuated liquid metal switch of the liquid metal to electrode configuration, tilting of the switch envelope from a normal substantially horizontal position causes movement of the pool of liquid metal toward and into engagement with the switching electrode. Reverse tilting of course causes reverse movement of the pool and disengagement from the electrode. The amount of tilting required between switch closure and switch opening is of course known as the differential of the switch.

In liquid metal switch applications where the switch is actuated by a non-resilient driver, the differential of the application can be taken to be the same as the differential of the switch per se. However, in other liquid metal switch applications, the differential of the application is greater than the differential of the switch per se due to the occurrence of an uncontrollable excess movement of the pool of liquid metal caused by the utilization of resilient driving means. Thus, in thermostats utilizing a spiral bimetal as a combined temperature sensing means and liquid metal switch driving means to cause actuation and deactuation of the switch, the cen- 'ter of gravity of the pool must be moved from one side of the vertical center line of the bimetal, to the center line where the horizontal position of the switch occurs, and there past. Upon moving past the horizontal position of the switch, the pool moves to an extreme position within the switch envelope because the weight of the pool overcomes the resilience of the bimetal. This movement of the pool is hereinafter identified as mass shift". It is apparent that such a mass shift increases the differential of the application over the differential of the switch per se.

I have directed my attention to alleviating the problem posed by mass shift and in so doing conceived the present invention. With my invention and when used in the thermostat application above referred to, the switch in the deactuating mode need not be moved so that the center of gravity of the pool passes the vertical center line of the spiral bimetal, as disengagement of the pool from the switching electrode takes place prior to the horizontal position of the switch being attained.

In other words, disengagement takes place at a negative break angle".

More specifically and as disclosed in the preferred embodiment, my invention is directed to a tilt actuated mercury switch of the mercury to electrode type including an elongated tubular glass envelope having a switching electrode and a pool depressor supported thereby with a pool of mercury disposed therein. The depressor and the pool are arranged so that with the switch in a normally substantially horizontal position interaction of the pool and the depressor sets up a restoring force tending to move the pool away from the electrode. Upon tilting of the switch in the actuating mode, the restoring force and the adhesional force between the pool of mercury and the interior surface of the envelope is overcome by gravitational force with the consequent movement of the pool into engagement with the electrode. Upon reverse tilting in the deactuating mode, movement of the pool away from the electrode takes place prior to the horizontal position of the switch being attained as the restoring force at this point is in excess of the summation of the adhesional force and the gravitational force. Consequently, switch opening takes place at a negative break angle.

It follows that if such a liquid metal switch as just described is utilized in the thermostat application set forth previously that no mass shift need be involved as the center of gravity of the pool would not have to be moved past the vertical center line of the bimetal during its excursions between the actuating and deactuating modes of the application. Therefore, the differential of the application and the differential of the switch per se can be considered to be the same which means a more precise control of the space being monitored by the thermostat is possible where a liquid metal switch incorporating my invention is utilized than is the case where a comparable prior art liquid metal switch is utilized.

Therefore, it is an object of the present invention to provide a tilt actuated liquid metal switch of the liquid metal to electrode type which exhibits a negative break angle.

This and other objects will become apparent from a reading of the following specification and claims taken in conjunction with the drawing in which:

FIG. 1, is a top view ofa liquid metal switch incorporating the invention;

FIG. 2 is a side view of the switch of FIG. 1;

FIG. 3 is a view of the switch showing the various forces of the system;

- FIGS. 4 and 5 show two conditions of a liquid metal switch of the prior art in a thermostat application; and

FIGS. 6 and 7 show two conditions of the liquid metal switch incorporating the invention hereof in the thermostat of FIGS. 4 and 5.

Referring now to the drawing and in particular to FIGS. 1 and 2, a tilt actuated liquid metal switch 10 of the liquid metal to electrode type is shown. The switch .includes a cylindrical envelope 12 which may be formed of potash soda lead glass. A switching electrode 14 having a cylindrical extremity and a pool depressor 16 having a spherical extremity are supported by the envelope 12 in conventional fashion. The electrode 14 but for the cylindrical extremity and the depressor 16 which also functions as an electrode may be fabricated from a nickel-iron alloy. The cylindrical extremity of the electrode 14 may be fabricated from molybdenum. A pool of liquid metal 18 which may be mercury is disposed within the envelope 12 for association with the electrode 14 and the depressor 16.

With the switch 10 in the normal substantially horizontal position, the spherical extremity of the depressor 16 engages the pool 18, and due to the interaction between the depressor and the surface tension of the pool, a surface restoring force tending to cause the pool to return to its free form shape results tending to remove the pool to an extremity of the envelope 12 away from the electrode 14. This force is hereinafter identified as the restoring force". Other forces in the system are the adhesional force between the engaging surfaces of the envelope l2 and the pool 18 which inhibits movement of the pool in either direction and, of course, gravitational force.

The forces just referred to are shown diagrammatically in FIG. 3. Thus, the restoring force R is shown associated with the depressor l6 and the pool 18. Further, the effective gravitational force G, is shown associated with the pool 18 as is the true gravitational force G. Also, the adhesional forces A which inhibits movement of the pool 18 in the actuating mode of the switch 10 and A which inhibits movement of the pool in the deactuating mode of the switch are shown associated with the engaging surfaces of the pool and of the envelope l2. As shown in FIG. 3, the switch 10 is shown in an exaggerated actuating mode where the adhesional force A comes into play and the adhesional force A is of no effect. Upon reverse tilting of the switch 10 taking place, adhesional force A,, comes into play and A is of no effect.

Still referring to FIG. 3, it will be appreciated that tilting of the switch 10 in a counterclockwise movement about an axis transverse to the longitudinal axis of the envelope 12 will ultimately cause the effective gravitational force G to exceed the adhesional force A, and the restoring force R whereupon the pool 18 will move toward and ultimately make engagement with the cylindrical extremity of the electrode 14 while still being in engagement with the spherical extremity of depressor 16 thereby allowing for the establishment of an electrical circuit across the electrode, the pool and the depressor.

Upon reverse tilting of the switch 10, the pool 18 is under the influence of the forces G A and R. Because of the arrangement of the elements of the switch 10, the pool 18 begins moving and ultimately becomes disengaged from the cylindrical extremity of the electrode 14 prior to the horizontal position of the switch being attained. This is because at this point the restoring force R exceeds the summation of the effective gravitational force G and adhesional force A This results in the switch 10 having a negative break angle.

In a practical application of my invention, comparable to that shown in FIGS. 1-3, I utilized an envelope formed of Coming 0012 glass having an inside diameter of 0.290 inches with a switching electrode less the cylindrical extremity and a depressor comprised of 52 nickel-iron glass sealing alloy. The cylindrical extremity of the electrode was formed of molybdenum to insure against wetting by the pool of mercury which weighed 2.9 grams. To reduce the adhesional forces, the interior surface of the envelope was etched as taught by the Hyzer et al -U.S. Pat. No. 3,174,885. The electrode and the depressor were disposed on the center line of the envelope as viewed in FIG. 2. The spherical portion of the depressor was of 0.093 inches diameter and, as viewed in FIG. 1, offset from the center line by 0.005 inches. The switching electrode was so placed that at the point of disengagement of the pool therefrom in the deactuating mode, the center of gravity of the pool was to the far side of the spherical extremity of the depressor thereby insuring that the restoring force acted in a manner assisting switching opening.

Mercury switches in general find practical applications in bimetal driven heating thermostats. Thus, referring to FIGS. 4 and 5, a spiral bimetal 20 appropriately supports a mercury'switch 22 having a pool of mercury 24 for association with a pair of electrodes 26 and 28. With the switch 22 in the condition of FIG. 4,

it is in an actuating mode and is asking for heat. As the temperature of the space being monitored rises, the bimetal 20 contracts causing a clockwise rotation of the switch 22. The actuated condition of the switch 22 continues at least until the horizontal position of the switch is attained because there are no forces in the system to overcome the adhesional force and the effective gravitational force. Ultimately the pool 24 does move away from the electrode 26 but in so moving the center of gravity thereof passes the vertical center line of the bimetal 20 and ultimately the switch 22 and the pool assume the position shown in FIG. 5 whereby a mass shift of the pool has resulted. Of course with the switch 22 moving in the actuating mode from the position shown in FIG. 5, the bimetal 20 must introduce sufficient force to move the switch first back to the horizontal position and then introduce further force to move the switch to cause switch closure. Because of the introduction of the mass shift of the pool 24, the differential of the arrangement including the bimetal 20 and the switch 22 is exaggerated and is greater than that of the switch per se.

By utilizing my invention, the problem of mass shift can be eliminated. Thus, referring now to FIGS. 6 and 7, a spiral bimetal 20 like that of FIGS. 4 and 5 supports a mercury switch 10 of the type described in regard to FIGS. 1-3. With the switch 10 in the actuating mode of FIG. 6 and asking for heat, ultimately the temperature of the space being monitored rises causing the bimetal 20 to contract resulting in the switch being moved in a clockwise direction. As this movement continues, ultimately the restoring force exceeds the summation of the effective gravitational force and the adhesional force whereupon the pool 18 disengages from the electrode 14. The disengagement takes place prior to the switch attaining a horizontal position as is shown in FIG. 7. It will be noted that under this set of conditions there need be no mass shift of the pool past the vertical center line of the bimetal 20 which means the bimetal will not have to expend force to return the switch 10 to the horizontal position as was the case above, noting particularly FIG. 5. Consequently, the differential of the arrangement including the bimetal 20 and the switch 10 of FIGS. 6 and 7 approaches the differential of the switch per se allowing for an increased control of the condition being monitored.

From the foregoing, it will be appreciated that I have provided a negative break angle tilt actuated liquid metal switch of the liquid metal to electrode type. The scope of my contribution should be determined from the following claims.

I claim:

I. A tilt actuated liquid metal switch comprising: an envelope having an interior surface normally maintained in a substantially horizontal position; a switching electrode supported by and extending into said envelope; a pool of liquid metal disposed within said envelope and engaging said interior surface; and a pool depressor provided within said envelope; said depressor including a portion located, with said envelope in the horizontal position. so as to be normally in engagement with a portion of said pool and so as to be disposed between said electrode and the center of gravity of said pool causing a restoring force, due to the interaction of the depressor portion and the surface tension of said pool, tending to move said pool away from said electrode; tilting of said envelope away from the horizontal position causing movement of said pool into engagement with said electrode due to gravitational force overcoming tee summation of adhesional force, set up by the engaging surfaces of said envelope and said pool,

and the restoring force; subsequent reverse tilting of 5 said envelope causing disengagement of said pool from said electrode prior to the horizontal position being attained due to the restoring force exceeding the summation of gravitational force and adhesional force.

2. The arrangement of claim 1 wherein said envelope is formed of an insulating material and said pool deof liquid metal is mercury. 

1. A tilt actuated liquid metal switch comprising: an envelope having an interior surface normally maintained in a substantially horizontal position; a switching electrode supported by and extending into said envelope; a pool of liquid metal disposed within said envelope and engaging said interior surface; and a pool depressor provided within said envelope; said depressor including a portion located, with said envelope in the horizontal position, so as to be normally in engagement with a portion of said pool and so as to be disposed between said electrode and the center of gravity of said pool causing a restoring force, due to the interaction of the depressor portion and the surface tension of said pool, tending to move said pool away from said electrode; tilting of said envelope away from the horizontal position causing movement of said pool into engagement with said electrode due to gravitational force overcoming tee summation of adhesional force, set up by the engaging surfaces of said envelope and said pool, and the restoring force; subsequent reverse tilting of said envelope causing disengagement of said pool from said electrode prior to the horizontal position being attained due to the restoring force exceeding the summation of gravitational force and adhesional force.
 2. The arrangement of claim 1 wherein said envelope is formed of an insulating material and said pool depressor is in the form of a second electrode allowing for an electrical circuit to be set up across said electrodes when both are engaged by said pool of liquid metal.
 3. The arrangement of claim 2 wherein said envelope is of elongated tubular configuration and the tiltinG thereof takes place about an axis transverse to the longitudinal axis thereof.
 4. The arrangement of claim 3 wherein said elongated tubular envelope is formed of glass and said pool of liquid metal is mercury. 